Methods and systems for dopant activation using microwave radiation

ABSTRACT

A semiconductor structure includes a substrate, a source/drain (S/D) junction, and an S/D contact. The S/D junction is associated with the substrate and includes a trench-defining wall, a semiconductor layer, and a semiconductor material. The trench-defining wall defines a trench. The semiconductor layer is formed over the trench-defining wall, partially fills the trench, substantially covers the trench-defining wall, and includes germanium. The semiconductor material is formed over the semiconductor layer and includes germanium, a percentage composition of which is greater than a percentage composition of the germanium of the semiconductor layer. The S/D contact is formed over the S/D junction.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of U.S. patent application Ser. No.15/488,657, filed Apr. 17, 2017, which is a continuation of U.S. patentapplication Ser. No. 15/217,024, filed Jul. 22, 2016, now U.S. Pat. No.9,627,212, which is a continuation of U.S. patent application Ser. No.14/688,002, filed Apr. 16, 2015, now U.S. Pat. No. 9,401,274, which is acontinuation-in-part of U.S. patent application Ser. No. 13/963,043,filed Aug. 9, 2013, now U.S. Pat. No. 9,012,315, all of which areincorporated herein by reference in their entirety.

FIELD

The technology described in this patent document relates generally tosemiconductor materials and more particularly to processing ofsemiconductor materials.

BACKGROUND

Fabrication of semiconductor devices often involves many process steps.For example, the process of fabricating a field effect transistorusually includes doping a semiconductor substrate (e.g., adding desiredimpurities into the substrate) to form source/drain junctions. Manydifferent methods may be implemented for doping the substrate, such asion implantation, diffusion, and epitaxial growth. Further, the dopantsintroduced into the substrate often need to be electrically activatedbefore semiconductor devices can be fabricated on the substrate. Theactivation of the dopants often includes dissolving dopant clusters, andtransferring the dopant atoms/molecules from interstitial positions intolattice sites of the lattice structure of the substrate. As an example,the dopants may be activated using rapid thermal annealing (RTA), ormillisecond thermal annealing (MSA).

Under certain circumstance, the fabrication process of semiconductordevices involves microwave radiation which typically includeselectromagnetic waves with wavelengths ranging from 1 m to 1 mm(corresponding to frequencies between 0.3 and 300 GHz). When microwaveradiation is applied to a certain material (e.g., a dielectric material)which includes electric dipoles, the dipoles change their orientationsin response to the changing electric fields of the microwave radiationand thus the material may absorb the microwave radiation to generateheat. The response of the material to the electric field of themicrowave radiation can be measured using a complex permittivity, ε(ω)*,which depends on the frequency of the electric field:ε(ω)*=ε(ω)′−iε(ω)″=ε₀(ε_(r)(ω)′−iε _(r)(ω)″)   (1)where ω represents the frequency of the electric field, ε(ω)′ representsa real component of the complex permittivity (i.e., a dielectricconstant), and ε(ω)″ represents a dielectric loss factor. In addition,ε₀ represents the permittivity of a vacuum, ε_(r)(ω)′ represents therelative dielectric constant, and ε_(r)(ω)″ represents the relativedielectric loss factor.

Whether a material can absorb the microwave radiation can becharacterized using a loss tangent, tan&

$\begin{matrix}{{\tan\mspace{11mu}\delta} = \frac{{ɛ^{''}\mu^{\prime}} - {ɛ^{\prime}\mu^{''}}}{{ɛ^{\prime}\mu^{\prime}} + {ɛ^{''}\mu^{''}}}} & (2)\end{matrix}$where μ′ represents a real component of the magnetic permeability of thematerial, and μ″ represents a magnetic loss factor. Assuming negligiblemagnetic loss (i.e., μ″=0), the loss tangent of a material is expressedas follows:

$\begin{matrix}{{\tan\mspace{11mu}\delta} = {\frac{ɛ^{''}}{ɛ^{\prime}} = \frac{ɛ_{r}^{''}}{ɛ_{r}^{\prime}}}} & (3)\end{matrix}$

Materials with a low loss tangent (e.g., tan δ<0.01) allow microwaves topass through with very little absorption. Materials with an extremelyhigh loss tangent (e.g., tan δ>10) reflect microwaves with littleabsorption. Materials with an intermediate loss tangent (e.g., 10≥tanδ>0.01) can absorb microwave radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an example diagram for dopant activation using microwaveradiation.

FIG. 2 depicts another example diagram for dopant activation usingmicrowave radiation.

FIG. 3 depicts an example diagram showing an apparatus for dopantactivation using microwave radiation.

FIG. 4 depicts an example diagram for dopant activation using microwaveradiation.

FIG. 5 depicts another example diagram for dopant activation usingmicrowave radiation.

FIG. 6 depicts an example flow chart for dopant activation usingmicrowave radiation.

FIG. 7 depicts another example flow chart for dopant activation usingmicrowave radiation.

FIG. 8 depicts an example flow chart of operation 770 of FIG. 7.

FIG. 9 depicts another example flow chart of operation 770 of FIG. 7.

FIG. 10 depicts another example flow chart of operation 770 of FIG. 7.

FIG. 11 depicts another example flow chart of operation 770 of FIG. 7.

FIG. 12 depicts an example plot showing concentration versus depth.

FIG. 13 depicts an example diagram showing a semiconductor structure.

DETAILED DESCRIPTION

The conventional technology for dopant activation, such as RTA and MSA,often involves high processing temperatures. For example, RTA is usuallyperformed at a temperature higher than 950° C., and MSA at a temperaturehigher than 1050° C. Such high processing temperatures may not besuitable for some modern semiconductor devices. For example, certainmaterials (e.g., germanium, tin) used in modern complementarymetal-oxide-semiconductor (CMOS) devices have low melting points, whichlimits the processing temperature for /fabricating the devices.

FIG. 1 depicts an example diagram for dopant activation using microwaveradiation. As shown in FIG. 1, an microwave-absorption material 102 isplaced at a distance (e.g., d) from a semiconductor structure 104 whichincludes dopants, where microwave radiation may be applied to both themicrowave-absorption material 102 and the semiconductor structure 104 inorder to activate the dopants in the semiconductor structure 104.

The semiconductor structure 104 which has a small loss tangent may notabsorb microwave radiation efficiently. On the other hand, themicrowave-absorption material 102 which has a larger loss tangent (e.g.,in a range of about 0.01 to about 2) may absorb sufficient microwaveradiation and increase an electric field density over the semiconductorstructure 104. At the raised electric field density, the loss tangent ofthe semiconductor structure 104 may increase, and the semiconductorstructure 104 may absorb the microwave radiation more efficiently sothat the dopants within the semiconductor structure 104 may be activatedfor fabrication of semiconductor devices.

For example, the semiconductor structure 104 may include a junction witha number of dopants. The junction including the dopants may be formed ona substrate at an elevated temperature (e.g., in a range of about 300°C. to about 600° C.) by epitaxial growth, for example, through chemicalvapor deposition (CVD). In response to the applied microwave radiation,the microwave-absorption material 102 intensifies the electric fielddensity over the semiconductor structure 104. More and more dipolesrelated to the dopants may be formed in the semiconductor structure 104,and these dipoles may vibrate and/or rotate in response to the appliedmicrowave radiation. The semiconductor structure 104 may absorb moremicrowave radiation under the increased electric field density. Once theelectric field density over the semiconductor structure 104 exceeds athreshold, the dipole formation and the dipole motions (e.g., vibrationand/or rotation) may eventually break down the bonds between the dopantsand the interstitial sites in the semiconductor structure 104, so thatthe dopants may be activated. The distance between themicrowave-absorption material 102 and the semiconductor structure 104may be adjusted to improve the dopant activation. For example, thedopants may include phosphorous, phosphorous-based molecules, germanium,helium, boron, boron-based molecules, or a combination thereof.

In one embodiment, the microwave radiation applied to themicrowave-absorption material 102 may have a frequency in the range ofabout 2 GHz to about 10 GHz. For example, the microwave-absorptionmaterial 102 may include boron-doped silicon germanium, siliconphosphide, titanium, nickel, silicon nitride, silicon dioxide, siliconcarbide, or a combination thereof. The microwave-absorption material 102may have a much larger size than the semiconductor structure 104 so thatthe electric field density may be approximately uniform over thesemiconductor structure 104. As an example, the semiconductor structure104 may include a semiconductor substrate, a semiconductor-on-insulatorstructure, or a semiconductor thin film structure.

In another embodiment, to control dopant diffusion, the temperature ofthe semiconductor structure 104 may be kept within a range of about 500°C. to about 600° C. For example, the microwave radiation may be appliedto the microwave-absorption material 102 and the semiconductor structure104 for a time period within a range of about 40 seconds to about 300seconds.

FIG. 2 depicts another example diagram for dopant activation usingmicrowave radiation. As shown in FIG. 2, a semiconductor structure 202including dopants is placed between two microwave-absorption materials204 and 206, where microwave radiation may he applied to thesemiconductor structure 202 and the microwave-absorption materials 204and 206 in order to activate the dopants in the semiconductor structure202. For example, the microwave-absorption materials 204 and 206 mayhave the same loss tangent or different loss tangents. As an example,the distance (e.g., d1) between the microwave-absorption material 204and the semiconductor structure 202 may be the same as or different fromthe distance (e.g., d2) between the microwave-absorption material 206and the semiconductor structure 202. The distances d1 and d2 may beadjusted to improve the dopant activation. In one embodiment, themicrowave-absorption material 204 may be placed above a top surface ofthe semiconductor structure 202, and the microwave-absorption material206 may be placed below a bottom surface of the semiconductor structure202. In another embodiment, the microwave-absorption material 204 may beplaced over a side surface of the semiconductor structure 202, and themicrowave-absorption material 206 may be placed over another sidesurface of the semiconductor structure 202. In yet another embodiment,multiple microwave-absorption materials may be placed above the topsurface, below the bottom surface, and over one or more side surfaces ofthe semiconductor structure 202.

FIG. 3 depicts an example diagram showing an apparatus for dopantactivation using microwave radiation. As shown in FIG. 3, asemiconductor structure 302 including dopants is placed between twomicrowave-absorption materials 304 and 306 within a shell 308. The shell308 includes one or more microwave ports 310 through which microwaveradiation may be introduced. For example, the shell 308 may be made of ametal material. The microwave-absorption materials 304 and 306 may bepre-heated to predetermined temperatures (e.g., in a range of about 500°C. to about 600° C.) by heat sources 312 and 314, respectively, so as toenhance absorption of microwave radiation by the microwave-absorptionmaterials 304, 306. For example, the heat sources 312 and 314 mayinclude an Ar lamp, a Xeon lamp, or a tungsten-halogen lamp. In anotherexample, the heat sources 312 and 314 may include one or more electricalpower sources (e.g., silicon-controlled rectifiers).

FIG. 4 depicts an example diagram for dopant activation using microwaveradiation. As shown in FIG. 4, a microwave-absorption layer 402 may beformed on a semiconductor structure 404 which includes dopants, wheremicrowave radiation may be applied to the microwave-absorption layer 402and the semiconductor structure 404. For example, themicrowave-absorption layer 402 may be formed on the semiconductorstructure 404 through epitaxial growth (e.g., CVD). The thickness of themicrowave-absorption layer 402 may be adjusted, e.g., between about 30nm and about 250 nm, to improve the dopant activation. For example, themicrowave-absorption layer 402 may be formed on the semiconductorstructure 404 through epitaxial growth (e.g., CVD). After the dopantactivation, the microwave-absorption layer 402 may be substantiallyremoved, for example, through etching (e.g., wet etching, dry etching)or chemical-mechanical polishing.

FIG. 5 depicts another example diagram for dopant activation usingmicrowave radiation. As shown in FIG. 5, a microwave-absorption layer502 may be formed on a top surface of a semiconductor structure 504which includes dopants, and another microwave-absorption layer 506 maybe formed on a bottom surface of the semiconductor structure 504.Microwave radiation may be applied to the semiconductor structure 504and the microwave-absorption layers 502 and 506 for dopant activation.In one embodiment, the microwave-absorption layer 502 may be formed on aside surface of the semiconductor structure 504, and themicrowave-absorption layer 506 may be formed on another side surface ofthe semiconductor structure 504. In another embodiment, multiplemicrowave-absorption layers may be formed on the top surface, on thebottom surface, and on one or more side surfaces of the semiconductorstructure 504.

FIG. 6 depicts an example flow chart for dopant activation usingmicrowave radiation. As shown in FIG. 6, at 602, a semiconductorstructure is provided, where the semiconductor structure includes aplurality of impurities, such as dopants. At 604, one or moremicrowave-absorption materials are provided. The microwave-absorptionmaterials are capable of increasing an electric field density associatedwith the semiconductor structure. At 606, microwave radiation is appliedto the microwave-absorption materials and the semiconductor structure toactivate the plurality of dopants for fabricating semiconductor devices.The microwave-absorption materials are configured to increase theelectric field density in response to the microwave radiation so as toincrease the semiconductor structure's absorption of the microwaveradiation to activate the dopants.

FIG. 13 depicts an example diagram showing a semiconductor structure,e.g., a fin field-effect transistor (FinFET). In one embodiment, atleast one of the semiconductor structures 104, 202, 404, 504 is aFinFET, e.g., the FinFET of FIG. 13. In another embodiment, the at leastone of the semiconductor structures 104, 202, 404, 504 is a planar FET.

FIG. 7 depicts another example flow chart for dopant activation usingmicrowave radiation, i.e., interfacial polarization heating. As shown inFIG. 7, at 710, a substrate, e.g., the substrate 1310 of FIG. 13, of asemiconductor structure, e.g., the semiconductor structure 104 of FIG.1, is received. As shown in FIG. 13, the substrate 1310 includes asurface 1310 a and a fin 1310 b that extends upward from the surface1310 a. In one embodiment, the substrate 1310 includes silicon,germanium, III-V compound, or a combination thereof. For example, thesubstrate 1310 includes about 95% silicon.

At 720, a gate electrode, e.g., the gate electrode 1320 of thesemiconductor structure of FIG. 13, is formed over the substrate 1310.In one embodiment, the gate electrode 1320 is a dummy gate electrode. Inanother embodiment, the gate electrode 1320 is a functional gateelectrode of a FinFET. As shown in FIG. 13, the gate electrode 1320includes a gate 1320 a that extends generally transverse to the fin 1310b and a spacer 1320 b that is provided on each side of the gate 1320 a.In one embodiment, the gate 1320 a is made of polysilicon or anysuitable metal material. Examples of metal materials include, but arenot limited to, Tin, TaN, ZrSi₂, MoSi₂, TaSi₂, NiSi₂, WN, and othersuitable p-type work function metal materials.

At 730, a trench is formed that extends into the fin 1310 b and that isdefined by a trench-defining wall, e.g., the trench-defining wall 1330of the semiconductor structure of FIG. 13. In one embodiment, the trenchhas a depth of between about 30 nm and about 70 nm from a surface of thefin 1310 b.

At 740, a semiconductor layer, e.g., the semiconductor layer 1340 of thesemiconductor structure of FIG. 13, is formed on the trench-definingwall 1330 to partially fill the trench. For example, the semiconductorlayer 1340 has a thickness of between about 5 nm and about 15 nm. In oneembodiment, the semiconductor layer 1340 includes germanium. Thesemiconductor layer 1340 may further include silicon, boron, or acombination thereof. For example, the semiconductor layer 1340 is madeof silicon germanium or silicon germanium doped with boron. In someembodiments, a percentage composition of the germanium of thesemiconductor layer 1340 is less than about 50%, e.g., about 35%. Insome embodiments, a concentration of the boron of the semiconductorlayer 1340 is between about 1E21 atoms/cm³ and about 5E21 atoms/cm³,e.g., about 3.7E21 atoms/cm³.

In one embodiment, operation 740 includes forming two or more sublayersof the semiconductor layer 1340 such that percentage compositions ofgermanium gradually increase from an outermost sublayer of the two ormore sublayers to an innermost sublayer of the two or more sublayers. Inanother embodiment, operation 740 includes forming two or more sublayersof the semiconductor layer 1340 such that concentrations of borongradually decrease from an outermost sublayer of the two or moresublayers to an innermost sublayer of the two or more sublayers.

At 750, a semiconductor material, e.g., the semiconductor material 1350of the semiconductor structure of FIG. 13, is formed on thesemiconductor layer 1340 to substantially fill the trench. In oneembodiment, the semiconductor material 1350 includes germanium. Thesemiconductor material 1350 may further include silicon, boron, or acombination thereof. For example, the semiconductor material 1350 ismade of silicon germanium or silicon germanium doped with boron. In someembodiments, a percentage composition of the germanium of thesemiconductor material 1350 is greater than a percentage composition ofgermanium of the semiconductor layer 1340. For example, the percentagecomposition of the germanium of the semiconductor material 1350 isbetween about 50% and about 95%. In some embodiments, a concentration ofthe boron of the semiconductor material 1350 is less than aconcentration of boron of the semiconductor layer 1340. For example, theconcentration of the boron of the semiconductor material 1350 is betweenabout 2E20 atoms/cm³ and about 1E21 atoms/cm³.

At 760, the semiconductor material 1350 is doped with boron such that anupper layer 1360 of the semiconductor material 1350 has a higherconcentration of the boron than a lower layer of the semiconductormaterial 1350. For example, the concentration of the boron of the upperlayer 1360 is between about 1E21 atoms/cm³ and about 5E21 atoms/cm³. Inone embodiment, the boron of the upper layer 1360 has a depth of betweenabout 5 nm and about 15 nm from the surface of the fin 1310 b.

It is noted that at least one of the trench-defining wall 1330, thesemiconductor layer 1340, and the semiconductor material 1350 constitutea source/drain (S/D) junction 1370 of the semiconductor structure 104.In one embodiment, the S/D junction 1370 and the gate 1320 a definetherebetween a distance of between about 1 nm and about 9 nm.

In some embodiments, the S/D junction 1370 is formed above a substrate,e.g., a bulk substrate or a silicon-on-insulator (SOI) substrate. Inother embodiments, the S/D junction 1370 extends from above into asubstrate.

At 770, the dopants, i.e., the germanium and the boron of thesemiconductor material 1350, are activated, in a manner that will bedescribed hereinafter.

FIG. 8 depicts an example flow chart of operation 770 of FIG. 7. Asshown in FIG. 8, at 810, a microwave-absorption material, e.g., themicrowave-absorption material 102 of FIG. 1, is received. At 820, themicrowave-absorption material 102 is adjusted at a distance, e.g.,distance d as shown in FIG. 1, from the semiconductor structure 104 soas to improve dopant activation. In one embodiment, the distance d isbetween about 2 mm and about 10 mm. At 830, microwave radiation isapplied to the microwave-absorption material 102 and the semiconductorstructure 104 so as to activate the dopants.

During operation 830, the microwave-absorption material 102 increasesabsorption of the microwave radiation by the boron of the upper layer1360 such that the boron of the upper layer 1360 generates heat at atemperature, e.g., higher than 1100° C., whereby the boron of the upperlayer 1360 is activated. As a result, a relatively high concentration ofthe activated boron, i.e., substantially the same as the concentrationof the boron of the upper layer 1360 prior to operation 770, is obtainedfor the upper layer 1360 of the semiconductor material 1350 of the S/Djunction 1370 of the semiconductor structure 104 of the presentdisclosure. FIG. 12 depicts an example plot showing concentration versusdepth. In one embodiment, as shown in FIG. 12, the concentration of theactivated boron of the upper layer 1360 of the semiconductor material1350 of the S/D junction 1370 of the semiconductor structure 104 isbetween about 1E21 atoms/cm³ and about 5E21 atoms/cm³. In anotherembodiment, the activated boron of the lower layer of the semiconductormaterial 1350 has substantially the same concentration as the boron ofthe lower layer of the semiconductor material 1350 prior to operation770. For example, the concentration of the activated boron of the lowerlayer of the semiconductor material 1350 is between about 2E20 atoms/cm³and about 1E21 atoms/cm³. In yet another embodiment, the activated boronof the semiconductor layer 1340 has substantially the same concentrationas the boron of the semiconductor layer 1340 prior to operation 770. Forexample, the concentration of the activated boron of the semiconductorlayer 1340 is between about 1E21 atoms/cm³ and about 5E21 atoms/cm³.

In addition, during operation 830, i.e., the application of themicrowave radiation to the microwave-absorption material 102 and thesemiconductor structure 104, crystal defects created from prioroperations are reduced and a relatively low crystal defect density isachieved for the activated germanium and the activated boron of thesemiconductor material 1350 of the S/D junction 1370 of thesemiconductor structure 104 of the present disclosure. In oneembodiment, the crystal defect density of the activated germanium of thesemiconductor material 1350 of the S/D junction 1370 of thesemiconductor structure 104 is less than about 1E12 atoms/cm³. Forexample, the crystal defect density of the activated germanium of thesemiconductor material 1350 of the S/D junction 1370 of thesemiconductor structure 104 is about 1E7 atoms/cm³. In anotherembodiment, the crystal defect density of the activated boron of theupper layer 1360 of the semiconductor material 1350 of the S/D junction1370 of the semiconductor structure 104 is between about 1E5 atoms/cm³and about 1E7 atoms/cm³.

In some embodiments, the activated germanium of the semiconductor layer1340 has substantially the same percentage composition, e.g., less thanabout 50%, as the germanium of the semiconductor layer 1340 prior tooperation 770. In other embodiments, the activated germanium of thesemiconductor material 1350 has substantially the same percentagecomposition, e.g., between about 50% and 95%, as the germanium of thesemiconductor material 1350 prior to operation 770.

Moreover, during operation 830, i.e., the application of the microwaveradiation to the microwave-absorption material 102 and the semiconductorstructure 104, the substrate 1310 is kept at a temperature between about500° C. and about 600° C. Thus, unlike the conventional technology fordopant activation, e.g., RTA, in which the entire semiconductorstructure is heated at a temperature higher than e.g., 950° C., theboron of the upper layer 1360 of the S/D junction 1370 of thesemiconductor structure 104 is selectively heated at a highertemperature, whereas the substrate 1310 of the semiconductor structure104 at a lower temperature. The substrate 1310 thus serves as a heatsinkand permits a temperature of the semiconductor structure 104 to rampdown at a faster rate. As a result, the activated boron of the upperlayer 1360 of the semiconductor material 1350 of the S/D junction 1370of the semiconductor structure 104 of the present disclosure has arelatively shallow depth, i.e., substantially the same as the depth ofthe boron of the upper layer 1360 prior to operation 770. In oneembodiment, as shown in FIG. 12, the activated boron of the upper layer1360 of the semiconductor material 1350 of the S/D junction 1370 of thesemiconductor structure 104 has a depth of between about 5 nm and about15 nm from a surface of the S/D junction 1370.

In an embodiment, after operation 770, i.e., the activation of thedopants, the S/D junction 1370 has a depth of between about 30 nm andabout 70 nm. In addition, after operation 770, the semiconductor layer1340 is maintained at substantially the same thickness, e.g., betweenabout 5 nm and about 15 nm. Moreover, after operation 770, as shown inFIG. 13, the S/D junction 1370 and the gate 1320 a define therebetween adistance d3 of between about 1 nm and about 9 nm.

Referring back to FIG. 7, at 780, an S/D contact, e.g., the S/D contact1380 of the semiconductor structure of FIG. 13, is formed on the S/Djunction 1370. Examples of materials for the S/D contact 1380 include,but are not limited to, tungsten, aluminum, titanium, nickel, cobalt,and the like.

It is noted that, since the semiconductor material 1350 of the S/Djunction 1370 has a high percentage composition of the germanium andsince the boron of the upper layer 1360 of the semiconductor material1350 of the S/D junction 1370 has a shallow depth and a highconcentration, the S/D contact 1380 and the S/D junction 1370 of thesemiconductor structure 104 of the present disclosure have a relativelylow contact resistivity therebetween. In one embodiment, the contactresistivity between the S/D contact 1380 and the S/D junction 1370 ofthe semiconductor structure 104 is less than about 5E-9 Ohms-cm². Forexample, the contact resistivity between the S/D contact 1380 and theS/D junction 1370 of the semiconductor structure 104 is about 8E-10Ohms-cm².

FIG. 9 depicts another example flow chart of operation 770 of FIG. 7. Asshown in FIG. 9, at 910, a pair of microwave-absorption materials, e.g.,the microwave-absorption materials 204, 206 of FIG. 2, between which thesemiconductor structure, e.g., the semiconductor structure 202 of FIG.2, is placed, are received. At 920, the microwave-absorption material204 is adjusted at a distance, e.g., distance d1 as shown in FIG. 2,from a surface of the semiconductor structure 202 so as to improvedopant activation. In one embodiment, the distance d1 is between about 2mm and about 10 mm. At 930, the microwave-absorption material 206 isadjusted at a distance, e.g., distance d2 as shown in FIG. 2, fromanother surface of the semiconductor structure 202 also to improvedopant activation. In one embodiment, the distance d2 is between about 2mm and about 10 mm. At 940, microwave radiation is applied to themicrowave-absorption materials 204, 206 and the semiconductor structure202 so as to activate the dopants.

FIG. 10 depicts another example flow chart of operation 770 of FIG. 7.As shown in FIG. 10, at 1010, a microwave-absorption material, e.g., themicrowave-absorption material 402 of FIG. 4, is formed on, e.g., inconformance with, a surface of the semiconductor structure, e.g., thesemiconductor structure 404 of FIG. 4. At 1020, a thickness of themicrowave-absorption material 402 is adjusted, e.g., between about 30 nmand about 250 nm, so as to improve dopant activation. At 1030, microwaveradiation is applied to the microwave-absorption material 402 and thesemiconductor structure 404 so as to activate the dopants. At 1040, themicrowave-absorption material 402 is removed, e.g., through wet etching,dry etching, chemical-mechanical polishing, or a combination thereof,from the semiconductor structure 404.

FIG. 11 depicts another example flow chart of operation 770 of FIG. 7.As shown in FIG. 11, at 1110, a first microwave-absorption material,e.g., the microwave-absorption material 502 of FIG. 5, is formed on,e.g., in conformance with, a surface of the semiconductor structure,e.g., the semiconductor structure 504 of the FIG. 5. At 1120, athickness of the microwave-absorption material 502 is adjusted, e.g.,between about 30 nm and about 250 nm, so as to improve dopantactivation. At 1130, a second microwave-absorption material, e.g., themicrowave-absorption material 506 of FIG. 5, is formed on, e.g., inconformance with, another surface of the semiconductor structure 504. At1140, a thickness of the microwave-absorption material 506 is adjusted,e.g., between about 30 nm and about 250 nm, also to improve dopantactivation. At 1150, microwave radiation is applied to themicrowave-absorption materials 502, 506 and the semiconductor structure504 so as to activate the dopants. At 1160, the microwave-absorptionmaterials 502, 506 are removed from the semiconductor structure 504.

In one embodiment, a lightly-doped S/D (LDD) associated with a substrateof a semiconductor structure is formed. The formation of an LDDincludes: doping a region of the semiconductor structure with aplurality of dopants; receiving a microwave-absorption material orforming the microwave-absorption material on the semiconductorstructure; adjusting the microwave-absorption material at a distancefrom the semiconductor structure or adjusting a thickness of themicrowave-absorption material; and applying microwave radiation to themicrowave-absorption material and the semiconductor structure.

In an embodiment, a semiconductor structure comprises a substrate, asource/drain (S/D) junction, and an S/D contact. The S/D junction isassociated with the substrate and includes a trench-defining wall thatdefines a trench, a semiconductor layer that is formed over thetrench-defining wall, that partially fills the trench, thatsubstantially covers the trench-defining wall, and that includesgermanium, and a semiconductor material that is formed over thesemiconductor layer and that includes germanium, a percentagecomposition of which is greater than a percentage composition of thegermanium of the semiconductor layer. The S/D contact is formed over theS/D junction.

In another embodiment, a semiconductor structure comprises a substrate,a source/drain (S/D) junction, and an S/D contact. The S/D junction isassociated with the substrate and includes a trench-defining wall, asemiconductor layer that is formed over the trench-defining wall andthat has a plurality of sublayers, and a semiconductor material that isformed over the semiconductor layer. A concentration of boron of anoutermost sublayer of the sublayers is greater than a concentration ofboron of an innermost sublayer of the sublayers. The S/D contact isformed over the SD junction.

In another embodiment, a source/drain (S/D) junction comprises asemiconductor layer and a semiconductor material. The semiconductorlayer is formed on a substrate and includes germanium. And asemiconductor material that is formed over the semiconductor layer andincludes germanium. The percentage composition of the semiconductormaterial is greater than a percentage composition of the germanium ofthe semiconductor layer.

In another embodiment, a semiconductor structure comprising a S/Djunction associated with a substrate and a S/D contact. The S/D junctionincludes a semiconductor layer and a semiconductor material having aplurality of sub-layers. The S/D contact is formed over the S/Djunction. The sublayers include a concentration of boron of an outermostsub-layer greater than a concentration of boron of an innermostsub-layer of the plurality of sub-layers. The semiconductor material isover the semiconductor layer.

in another embodiment, a method comprises providing a semiconductorstructure that includes a substrate, forming a source/drain (S/D)junction, and forming an S/D contact over the semiconductor material.Forming the S/D junction includes: forming in the substrate a trenchthat is defined by a trench-defining wall; forming over thetrench-defining wall a semiconductor layer that partially fills thetrench, that substantially covers the trench-defining wall, and thatincludes germanium; and forming over the semiconductor layer asemiconductor material that includes germanium, a percentage compositionof which is greater than a percentage composition of the germanium ofthe semiconductor layer.

In another embodiment, a method comprises forming a source/drainjunction above a substrate, forming over the substrate a semiconductorlayer that includes germanium, and forming over the semiconductor layera semiconductor material that includes germanium, and forming an S/Dcontact over the S/D junction. The percentage composition thesemiconductor material is greater than a percentage composition of thegermanium of the semiconductor layer.

This written description uses examples to disclose the invention,include the best mode, and also to enable a person skilled in the art tomake and use the invention. The patentable scope of the invention mayinclude other examples that occur to those skilled in the art. Oneskilled in the relevant art will recognize that the various embodimentsmay be practiced without one or more of the specific details, or withother replacement and/or additional methods, materials, or components.Well-known structures, materials, or operations may not be shown ordescribed in detail to avoid obscuring aspects of various embodiments ofthe invention. Various embodiments shown in the figures are illustrativeexample representations and are not necessarily drawn to scale.Particular features, structures, materials, or characteristics may becombined in any suitable manner in one or more embodiments. Variousadditional layers and/or structures may be included and/or describedfeatures may be omitted in other embodiments. Various operations may bedescribed as multiple discrete operations in turn, in a manner that ismost helpful in understanding the invention. However, the order ofdescription should not be construed as to imply that these operationsare necessarily order dependent. In particular, these operations neednot be performed in the order of presentation. Operations describedherein may be performed in a different order, in series or in parallel,than the described embodiment. Various additional operations may beperformed and/or described. Operations may be omitted in additionalembodiments.

This written description and the following claims may include terms,such as left, right, top, bottom, over, under, upper, lower, first,second, etc. that are used for descriptive purposes only and are not tobe construed as limiting. For example, terms designating relativevertical position may refer to a situation where a device side (oractive surface) of a substrate or integrated circuit is the “top”surface of that substrate; the substrate may actually be in anyorientation so that a “top” side of a substrate may be lower than the“bottom” side in a standard terrestrial frame of reference and may stillfall within the meaning of the term “top.” The term “on” as used herein(including in the claims) may not indicate that a first layer “on” asecond layer is directly on and in immediate contact with the secondlayer unless such is specifically stated; there may be a third layer orother structure between the first layer and the second layer on thefirst layer. The term “under” as used herein (including in the claims)may not indicate that a first layer “under” a second layer is directlyunder and in immediate contact with the second layer unless such isspecifically stated; there may be a third layer or other structurebetween the first layer and the second layer under the first layer. Theembodiments of a device or article described herein can be manufactured,used, or shipped in a number of positions and orientations. Personsskilled in the art will recognize various equivalent combinations andsubstitutions for various components shown in the figures.

What is claimed is:
 1. A method comprising: etching a source/draintrench in a substrate; forming a first semiconductor layer in thesource/drain trench, wherein the first semiconductor layer partiallyfills the source/drain trench; forming a second semiconductor layer overthe first semiconductor layer in the source/drain trench, wherein thesecond semiconductor layer fills a remaining portion of the source/draintrench, the first semiconductor layer includes a first concentration ofa dopant, the second semiconductor layer includes a second concentrationof the dopant, the second concentration of the dopant is different thanthe first concentration of the dopant, and the first semiconductor layerand the second semiconductor layer form a source/drain feature; andactivating the dopant by: placing a microwave-absorption material adistance from the source/drain feature, and applying microwave radiationto the microwave-absorption material and the source/drain feature. 2.The method of claim 1, wherein the distance is about 2 mm to about 10mm.
 3. The method of claim 1, wherein the applying the microwaveradiation to the microwave-absorption material and the source/drainfeature includes heating the substrate to a temperature of about 500° C.to about 600° C.
 4. The method of claim 1, wherein the applying themicrowave radiation to the microwave-absorption material and thesource/drain feature includes heating the second semiconductor layer toa temperature of greater than about 1,100° C.
 5. The method of claim 1,wherein the microwave radiation has a frequency of about 2 GHz to about10 GHz.
 6. The method of claim 1, wherein the microwave radiation isapplied to the microwave-absorption material and the source/drainfeature for about 40 seconds to about 300 seconds.
 7. The method ofclaim 1, wherein the placing the microwave-absorption material thedistance from the source/drain feature includes placing themicrowave-absorption material the distance above the secondsemiconductor layer.
 8. The method of claim 1, wherein themicrowave-absorption material includes a first microwave-absorptionmaterial and a second microwave-absorption material and the placing themicrowave-absorption material the distance from the source/drain featureincludes: placing the first microwave-absorption material a firstdistance above the second semiconductor layer, and placing the secondmicrowave-absorption material a second distance below the secondsemiconductor layer.
 9. The method of claim 1, wherein the firstconcentration of the dopant is the same before and after the applyingthe microwave radiation and the second concentration of the dopant isthe same before and after the applying the microwave radiation.
 10. Themethod of claim 1, further comprising, before applying the microwaveradiation, pre-heating the microwave-absorption material.
 11. A methodcomprising: etching a source/drain trench in a substrate; forming afirst semiconductor layer in the source/drain trench, wherein the firstsemiconductor layer partially fills the source/drain trench; forming asecond semiconductor layer over the first semiconductor layer in thesource/drain trench, wherein the second semiconductor layer fills aremaining portion of the source/drain trench, the first semiconductorlayer includes a first concentration of a dopant, the secondsemiconductor layer includes a second concentration of the dopant, thesecond concentration of the dopant is different than the firstconcentration of the dopant, and the first semiconductor layer and thesecond semiconductor layer form a source/drain feature; and activatingthe dopant by: epitaxially growing a microwave-absorption material overthe source/drain feature, and after applying microwave radiation to themicrowave-absorption material and the source/drain feature, removing themicrowave-absorption material.
 12. The method of claim 11, wherein athickness of the microwave-absorption material is about 30 nm to about250 nm.
 13. The method of claim 11, wherein the applying the microwaveradiation to the microwave-absorption material and the source/drainfeature includes heating the substrate to a temperature of about 500° C.to about 600° C.
 14. The method of claim 11, wherein the applying themicrowave radiation to the microwave-absorption material and thesource/drain feature includes heating the second semiconductor layer toa temperature of greater than about 1,100° C.
 15. The method of claim11, wherein the microwave radiation has a frequency of about 2 GHz toabout 10 GHz.
 16. The method of claim 11, wherein the microwaveradiation is applied to the microwave-absorption material and thesource/drain feature for about 40 seconds to about 300 seconds.
 17. Themethod of claim 11, wherein epitaxially growing the microwave-absorptionmaterial over the source/drain feature includes epitaxially growing themicrowave-absorption material on the second semiconductor layer.
 18. Themethod of claim 11, wherein the microwave-absorption material includes afirst microwave-absorption material and a second microwave-absorptionmaterial and epitaxially growing the microwave-absorption material overthe source/drain feature includes: epitaxially growing the firstmicrowave-absorption material on a surface of the second semiconductorlayer, and epitaxially growing the second microwave-absorption materialon a surface of the substrate.
 19. A method comprising: etching asource/drain trench in a fin; forming a firstsilicon-and-germanium-containing layer in the source/drain trench,wherein the first silicon-and-germanium-containing layer partially fillsthe source/drain trench; forming a secondsilicon-and-germanium-containing layer over the firstsilicon-and-germanium-containing layer in the source/drain trench,wherein the second silicon-and-germanium-containing layer fills aremaining portion of the source/drain trench, the firstsilicon-and-germanium-containing layer includes a first concentration ofboron, the second silicon-and-germanium-containing layer includes asecond concentration of boron, the second concentration of boron isdifferent than the first concentration of boron, and the firstsilicon-and-germanium-containing layer and the secondsilicon-and-germanium-containing layer form a source/drain feature; andactivating the boron by: placing a microwave-absorption material adistance from the source/drain feature, and applying microwave radiationto the microwave-absorption material and the source/drain feature. 20.The method of claim 19, wherein the first concentration of boron is thesame before and after the applying the microwave radiation and thesecond concentration of boron is the same before and after the applyingthe microwave radiation.